A communications network supplies a communication path between two or more end users. The network typically has the capacity to connect only a finite amount of communication traffic at any given instant. Each call consumes some portion of the total available communication resources. Moreover, the network must dedicate some of its resources to the management of the network. This management includes, for example, the setting up of calls, the defining of communication paths, and the communication of billing data within the network. The minimization of resources dedicated to managing the network is desirable so that more resources become available for providing communication services to paying subscribers of the network.
A network may be viewed as having a number of switching nodes. Each switching node receives communications from several input ports and distributes these communications among several output ports. The end parties to a call communicate directly with their respective nodes. In some cases, the calling and called parties utilize the same network node. However, in other cases communication paths are established between diverse nodes, perhaps through intermediary nodes.
When a communications network is configured so that the switching nodes and the end users are stationary, the network resources dedicated to managing the network are relatively minor. Network resources need not be consumed to locate end users because end users do not move. Once a communication path has been established between network nodes, the path need not change because the nodes and end users do not move. However, when the network accommodates mobile end users, the need to conserve network resources increases. When mobile end users are involved, RF links are typically used to communicate with the end users. These RF links represent scarce resources which must be conserved to the maximum extent possible. Since the end users are mobile, the locations of called parties cannot be determined simply by examining data describing the called parties' identities. Hence, additional network resources must be consumed and additional intelligence must be designed into the network to determine how to service a "roaming" subscriber whose location varies.
The conservation of network resources becomes especially difficult in a network where at least some of the switching nodes of the network are mobile themselves. This situation occurs when satellites in moving orbits are used as network switching nodes. In this situation, the selection of particular network switching nodes to use in establishing communication paths depends upon which satellites are in convenient locations at the instant a communication is delivered. Moreover, the communication path definitions change from instant to instant as the satellites travel in their orbits. This instant-to-instant change can simultaneously affect thousands or even millions of communication paths through the network. The network resources needed to coordinate the instant-to-instant changes for a multitude of communication paths can potentially be great enough to make operation of the network impractical.
Increased intelligence could be designed into mobile switching nodes (satellites) to compensate for instant-to-instant communication path changes. However, more simple satellite designs are highly desirable to reduce network costs. In addition, simple satellite designs provide the most cost-effective network reliability because the repair of orbiting satellites is prohibitively expensive. Due to a desire to keep satellite designs simple, the complex intelligence which manages the network is preferably located, as much as practical, in nodes of the network which are not mobile.